Semiconductor ceramic composition and ptc thermistor

ABSTRACT

A semiconductor ceramic composition which includes a compound represented by the following formula (1) as a main component, (Ba 1-x-y-w Bi x A y RE w ) m (Ti 1-z TM z )O 3  (1) (wherein, A is at least one element selected from Na or K, RE is at least one element selected from the group consisting of Y, La, Ce, Pr, Nd, Sm, Gd, Dy and Er, TM is at least one element selected from the group consisting of V, Nb and Ta, w, x, y, z and m satisfy the following relationships of (2)˜(5), 0.007≦x≦0.125 (2), x&lt;y≦2.0x (3), 0≦(w+z)≦0.01 (4), 0.94≦m≦0.999 (5)). And the semiconductor ceramic composition includes Ca in a proportion of 0.01˜0.055 mol in terms of element relative to 1 mol of Ti sites.

The present invention relates to a semiconductor ceramic composition andPTC thermistor, which may be used in a heater element or an overheatdetection sensor and the like.

BACKGROUND

As a thermistor, a PTC (Positive Temperature Coefficient) thermistorwith a positive temperature coefficient of resistance α has been known.The PTC thermistor will have an increase in the resistance against theincrease of the temperature, thus it can be used as a heater, an overcurrent protection element, an overheat detection sensor and the like.In the prior art, a PTC thermistor has been obtained by adding a minuteamount of rear earth elements and the like to barium titanate (BaTiO₃)which is the main component and forming it to a semiconductor.Therefore, it will have a sharp increase in the resistance by severalorders of magnitude above the Curie temperature, while it has a lowresistance under Curie temperature.

The Curie temperature of BaTiO₃ is usually 120° C. However, it can beshifted to a lower temperature by substituting a part of Ba with Sr orSn. As for the shift of the Curie temperature to be higher, it has beenrealized by substituting a part of Ba with Pb at present. From the viewpoint of the trend of decreasing the environmental load of the world,practical application of a substitute material with no Pb has beendemanded.

In the following Patent Document 1, a method for producing asemiconductor ceramic composition has been disclosed. In the method, oneor more of any of Nb, Ta or a rare earth element are added into asemiconductor ceramic composition consisting of Ba_(1-2X)(BiNa)_(X)TiO₃(0<X≦0.15), in which a part of Ba is substituted with (Bi, Na) ratherthan Pb. Then, after the composition is sintered in nitrogen, it isheat-treated in an oxidation atmosphere.

In addition, in the following Patent Document 2, a method for producinga semiconductor ceramic composition has been disclosed. In the method,the sintered body of a semiconductor ceramic composition in which a partof Ba of BaTiO₃ is substituted with (Bi, Na), is applied to aheat-treatment under a temperature below 600° C. in air atmosphere afterelectrodes are formed on it, as a means to increase the change ratio ofthe increased resistance above the Curie temperature to the specificresistance at a normal temperature (herein after, referred as“temperature coefficient of resistance α”).

Further, in the following Patent Document 3, a semiconductor ceramiccomposition without Pb has been disclosed. The composition is producedby preparing BT calcined powder consisting of (BaR)TiO₃ (wherein, R isat least one of rare earth elements) calcined powder or Ba(TiM)O₃(wherein, M is at least one of Nb or Sb) calcined powder, and BNTcalcined powder consisting of (BiNa)TiO₃ calcined powder, respectively,sintering the molded body prepared from the mixed calcined powders ofthe BT calcined powder and the BNT calcined powder in an atmospherecontaining 1 vol % or less of oxygen, then applying the sintered body toa heat-treatment for 0.5 hours or more and 24 hours or less under atemperature of 300° C. or more and 600° C. or less in an atmospherecontaining 0.1 vol % or more of hydrogen.

All of the above mentioned Patent documents have disclosed that, asemiconductor ceramic composition without using Pb, which has a Curietemperature shifted to a temperature higher than 120° C., a smallspecific resistance at a normal temperature, and a large temperaturecoefficient of resistance α, can be obtained.

PATENT DOCUMENTS

Patent Document 1: JPS56-169301A

Patent Document 2: JP2009-227477A;

Patent Document 3: JP2010-168265A;

SUMMARY

In the examples of the above mentioned Patent Document 1, the results ofheat-treatment carried out in the oxidation atmosphere after adding Ndto the semiconductor ceramic composition of Ba_(1-2X)(BiNa)_(X)TiO₃(0<X≦0.15) and sintering in nitrogen atmosphere has been disclosed.However, there is no detailed description regarding the case of addingother semiconducting agents, and it is not clear whether the performanceis improved or what is the degree of the improvement of the performance.Further, as semiconductor cannot be formed by sintering in airatmosphere, there is a problem that the production cost will beincreased compared to the case of sintering in air atmosphere.

Further, the semiconductor ceramic composition described in the abovementioned Patent Document 2 has a temperature coefficient of resistanceα of about 10%/° C. However, it is known that the specific resistance ata normal temperature and the temperature coefficient of resistance α arein a trade-off relationship, thus there is a problem that it will notswitch at the target temperature if the temperature coefficient ofresistance α is decreased. Therefore, a larger temperature coefficientof resistance α as well as a specific resistance at a normal temperaturesuitable for practical use is expected.

In the above mentioned Patent Document 3, it is disclosed that acomposition of BaTiO₃ with a part of Ba substituted by (Bi, Na) issintered in a nitrogen atmosphere or an argon atmosphere with an oxygenconcentration of less than 1 vol %, and then it is applied to aheat-treatment in a hydrogen atmosphere. However, as it cannot be madeinto a semiconductor by sintering in air atmosphere and a heat-treatmentis necessary after sintering, there is a problem that the productioncost will be increased compared to the case of sintering in the airatmosphere. Further, the temperature coefficient of resistance α of thesemiconductor ceramic composition described in Patent Document 3 isabout 8%/° C. However, a larger temperature coefficient of resistance αas well as a specific resistance at a normal temperature suitable forpractical use is expected.

In view of such actual circumstances, the present invention aims toprovide a BaTiO₃ based semiconductor ceramic composition without usingPb and with a Curie temperature shifted to higher than 120° C., whichcan be easily made into a semiconductor by sintering under any of an airatmosphere or a nitrogen atmosphere, and is excellent in the temperaturecoefficient of resistance α while having a specific resistance at anormal temperature maintained in a level suitable for practical use, andto provide a PTC thermistor.

The inventors of the present invention have performed various studies tosolve the problems, and have obtained a semiconductor ceramiccomposition which can be easily made into a semiconductor in a sinteringprocess under any of an air atmosphere or a nitrogen atmosphere, and hasa large temperature coefficient of resistance α and a Curie temperatureshifted to higher than 120° C., while having a specific resistance at anormal temperature suppressed to 10³ Ωcm or less, by using a specifiedconcentration of Bi and alkali metal A (Na or K) rather than Pb tosubstitute a part of Ba and adjusting the mole ratio of the Ba sites/Tisites and the additive amount of Ca to a specified range in the BaTiO₃based semiconductor ceramic composition.

The inventors believe that, as for the reasons for such performances, bycontrolling the ratio of Bi and alkali metal A (Na or K) in a way that Ais excessive, the excessive A will promote the forming of asemiconductor and will promote an appropriate grain growing as asintering agent. Therefore, a semiconductor ceramic composition with alow resistance can be obtained in a sintering process under any of anair atmosphere or a nitrogen atmosphere. In addition, a semiconductorceramic composition with excellent temperature coefficient of resistanceα can be obtained by controlling the mole ratio of Ba sites/Ti sites ina way that Ti sites is excessive and further controlling the additiveamount of Ca to a specified range which promote the grain growth.However, the mechanism for the forming of a semiconductor is notrestricted to this.

That is, the present invention relates to a semiconductor ceramiccomposition characterized in that it comprises a sintered body with amain component of BaTiO₃ based compound represented by the followingformula (1),

(Ba_(1-x-y-w)Bi_(x)A_(y)RE_(w))_(m)(Ti_(1-z)TM_(z))O₃  (1)

wherein, in the above formula (1), A is at least one element selectedfrom Na or K, RE is at least one element selected from the groupconsisting of Y, La, Ce, Pr, Nd, Sm, Gd, Dy and Er, TM is at least oneelement selected from the group consisting of V, Nb and Ta, w, x, y, z(the units of which are all mol) and m (the mole ratio of Ba sites/Tisites) satisfies the following relationships of (2)˜(5),

0.007≦x≦0.125  (2)

x<y≦2.0x  (3)

0≦(w+z)≦0.01  (4)

0.94≦m≦0.999  (5)

the sintered body comprises 0.01 mol or more and 0.055 mol or less of Cain terms of element relative to 1 mol of Ti sites.

In addition, said semiconductor ceramic composition preferably furthercomprises Si in a proportion of 0.035 mol or less in terms of elementrelative to 1 mol of Ti sites. An effect of decreasing the specificresistance at a normal temperature can be achieved by comprising Si insaid range.

Said semiconductor ceramic composition preferably further comprises Mnin a proportion of 0.0015 mol or less in terms of element relative to 1mol of Ti sites. An effect of improving the temperature coefficient ofresistance α can be achieved by comprising Mn in said range.

Further, the present invention also provides a PTC thermistor includingthe semiconductor ceramic composition. According to the presentinvention, a PTC thermistor such as a heater, an over current protectionelement, an overheat detection sensor or the like can be provided.

According to the present invention, in the BaTiO₃ based semiconductorceramic composition, a semiconductor ceramic composition which can beeasily made into a semiconductor in a sintering process under any of anair atmosphere or a nitrogen atmosphere, and has a small specificresistance at a normal temperature of 10³ Ωcm or less, a largetemperature coefficient of resistance α of 20%/° C. or more and a Curietemperature shifted to higher than 120° C., can be obtained. Thesemiconductor ceramic composition according to the present invention isparticularly suitable for overheat detection sensor, over currentprotection element, and heater.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic perspective view of the PTC thermistor of theembodiment of the present invention.

DETAILED DESCRIPTION OF EMBODIMENTS

FIG. 1 is a schematic perspective view of the PTC thermistor of oneembodiment of the present invention. PTC thermistor 1 consists of aceramic body 2 and electrodes 3 a and 3 b which are formed on the twoopposite main surfaces of the ceramic body. The ceramic body is asintered body, and is a semiconductor ceramic composition with a maincomponent of a BaTiO₃ based compound represented by the followingformula (1). On the other hand, Ni, Al, Cr or Ni—Cr alloy and the likecan be used as electrodes 3 a and 3 b.

The semiconductor ceramic composition of the present invention comprisesa compound represented by the following formula (1) as a main component,and further comprises Ca as a minor component.

(Ba_(1-x-y-w)Bi_(x)A_(y)RE_(w))_(m)(Ti_(1-z)TM_(z))O₃  (1)

(wherein, A is at least one element selected from Na or K, RE is atleast one element selected from the group consisting of Y, La, Ce, Pr,Nd, Sm, Gd, Dy and Er, TM is at least one element selected from thegroup consisting of V, Nb and Ta.)

In the above formula (1), w, x, y, z and m which represent thesubstituted amount of a part of Ba sites by Bi, A, and RE, thesubstituted amount of Ti sites by TM, and the ratio of Ba sites and Tisites respectively, satisfy the following relationships of (2)˜(5),wherein the substitution of Ba sites by RE and the substitution of Tisites by TM are arbitrary.

0.007≦x≦0.125  (2)

x<y≦2.0x  (3)

0≦(w+z)≦0.01  (4)

0.94≦m≦0.999  (5)

Further, in the composition represented by formula (1), 0.01 mol or moreand 0.055 mol or less of Ca in terms of element is comprised relative to1 mol of Ti sites.

In addition, said semiconductor ceramic composition preferably furthercomprises Si in a proportion of 0.035 mol or less, more preferably 0.005mol or more and 0.02 mol or less, in terms of element relative to 1 molof Ti sites. The Si precipitated in the grain boundaries can form acompound with an alkali metal A precipitated in a micro amount in thesame grain boundaries, and the movement of the alkali metal A ions whencharged can be suppressed. Thus, an effect of decreasing the specificresistance at a normal temperature is achieved. However, if the amountof Si exceeds 0.035 mol, the excessive Si element will precipitate in alarge amount in the grain boundaries, and will prevent the movement ofthe conducting electrons leading to the increase of the specificresistance at a normal temperature.

Further, said semiconductor ceramic composition preferably furthercomprises Mn in a proportion of 0.0015 mol or less, more preferably0.0005 mol or more and 0.001 mol or less, in terms of element relativeto 1 mol of Ti sites. When Mn is comprised in such a range, appropriateacceptor level is formed in the grain boundaries, and there is an effectof improving the temperature coefficient of resistance α. However, ifthe amount of Mn exceeds 0.0015 mol, the traps for the conductingelectrons will be excessive, and the specific resistance at a normaltemperature will increase.

In the formula (1), the amount range x of the component of Bi is0.007≦x≦0.125. The Curie temperature will not shift to a highertemperature when x is less than 0.007. In addition, if x exceeds 0.125,the forming to the semiconductor will be insufficient and the specificresistance at a normal temperature will be more than 10³ Ωcm. The Curietemperature of the present invention refers to the temperature underwhich the specific resistance of the element is twice compared to theone under 25° C.

In the formula (1), A is at least one element selected from Na or K, andthe amount range y of A is related to the amount range x of Bi whichsatisfies x<y≦2.0x. The forming to the semiconductor will beinsufficient and the specific resistance at a normal temperature will bemore than 10³ Ωcm, if y is not larger than x. If y is larger than 2.0x,excessive A will precipitate in a large amount in the grain boundaries,and prevent the movement of the conducting electrons and the specificresistance at a normal temperature will be more than 10³ Ωcm.

Moreover, between the case that said alkali metal A is Na and the casethat said alkali metal A is K, there will be some difference in theshift amounts of the Curie temperature to the higher temperature side,however, the variations of the specific resistance at a normaltemperature and the temperature coefficient of resistance α are almostthe same.

Additionally, in the formula (1), as for (w+z) which is the total amountof the donor components of RE and TM, if (w+z) is not large than 0.01mol relative to 1 mol of Ti sites, there is an effect of decreasing thespecific resistance at a normal temperature. And (w+z) may also be 0. Ifthe balances of specific resistance at a normal temperature and thetemperature coefficient of resistance α are considered, it is morepreferably 0.001 mol or more and 0.005 mol or less. If (w+z) exceeds0.01, the undissolved elements will precipitate in the grain boundaries,and inhibit the movement of the conducting electrons, and the specificresistance at a normal temperature will be more than 10³ Ωcm. Moreover,it is more preferable to select Sm, Gd, and Er as RE, and select Nb asTM. Further, it is preferred to add equal amounts of RE (Sm, Gd, Er) andTM (Nb). The effect of decreasing the specific resistance at a normaltemperature will be enhanced with the above donor components and theaddition methods.

In the formula (1), m (mole ratio of Ba sites/Ti sites) is preferably ina range of 0.94≦m≦0.999, and more preferably in a range of 0.95<m<0.96.The effect of decreasing the specific resistance at a normal temperaturewill be enhanced within such a range. The forming to the semiconductorwill be insufficient and the specific resistance at a normal temperaturewill be more than 10³ Ωcm, if m is less than 0.94. On the other hand, ifm exceeds 0.999, the density of the sintered body will decrease, and thespecific resistance at a normal temperature will be more than 10³ Ωcm.

Further, in addition to the BaTiO₃ based compound represented by saidformula (1), the semiconductor ceramic composition of the presentembodiment comprises Ca as a minor component. The amount range of theadded Ca is 0.01 mol or more and 0.055 mol or less in terms of elementrelative to 1 mol of Ti sites. And more preferably the range is 0.03 molor more and 0.04 mol or less. The specific resistance at a normaltemperature will be further decreased when the amount of Ca is in such arange.

If the amount range of Ca is less than 0.01 mol, the forming to thesemiconductor will be insufficient and the specific resistance at anormal temperature will be more than 10³ Ωcm. On the other hand, if theamount range of Ca exceeds 0.055 mol, the density of the sintered bodywill decrease, and the specific resistance at a normal temperature willbe more than 10³ Ωcm.

The semiconductor ceramic composition of the present embodiment isobtained by mixing and calcining the compounds comprising the elementswhich constitute the composition represented by the above formula,pulverizing the calcined powder, and then adding a binder to makegranulated powder and molding, debinding and sintering. The sinteringcan be carried out both in air atmosphere and nitrogen atmosphere.However, if it is carried out in nitrogen atmosphere, a furtherheat-treatment in an oxidation atmosphere under 800˜1000° C. isnecessary. Thus, sintering in air atmosphere is preferred from theviewpoint of simplifying the process.

The PTC thermistor is composed of a ceramic body which consists of thesemiconductor ceramic composition with BaTiO₃ based compound as a maincomponent, and electrodes which are Ni, Al, Cr or Ni—Cr alloy and thelike. The electrodes can be formed by plating, sputtering, screenprinting and the like. In addition, the shape of the PTC thermistor maybe a disc plate shape, a cuboid shape, or a laminated structure withseveral electrodes in the inner of the ceramic body.

EXAMPLES

Hereinafter, the present invention is further specifically describedbased on the examples and the comparative examples. However the presentinvention is not intended to be restricted by any of the followingexamples.

Example 1 (Samples NO. 1˜69), Comparative Example 1˜29

As for the starting materials, BaCO₃, TiO₂, Bi₂O₃, Na₂CO₃, K₂CO₃, CaCO₃,SiO₂, oxides of RE (for example, Y₂O₃), and oxides of TM (for example,Nb₂O₅) were prepared, and all the materials were weighed in a way thatthe composition after sintering would be as shown in tables 1˜7. Afterwet-mixed in acetone with a ball mill, the mixture was dried andcalcined for 2 hours under 900° C.

The calcined body was wet-pulverized in pure water using a ball mill,and after that dehydration and drying were carried out. Then it wasgranulated using binders such as PVA and the like to obtain granulatedpowder. The granulated powder was molded into a cylindrical shape(diameter of 17 mm×thickness of 1.0 mm) with a uniaxial press machine,and then sintered in air atmosphere under 1200° C. for 2 hours to obtaina sintered body.

Ag—Zn paste was coated by screen printing on the two surfaces of thesintered body and then baked in air atmosphere under 500˜700° C. Thenthe measuring of the specific resistance over temperature was carriedout from 25° C. to 280° C. The results of example 1 of the presentinvention was shown in tables 1˜5.

The temperature coefficient of resistance α was defined as the followingformula.

α=(ln R ₁−ln R _(C))×100/(T ₁ −T _(c))

Wherein, R₁ was the specific resistance under T₁, T₁ was the temperatureof T_(C)+20° C., Tc was the Curie temperature, and R_(C) was thespecific resistance under T_(C).

Example 2 Sample NO. 70

A semiconductor ceramic composition was prepared in the same way asExample 1, except that the atmosphere in the process of sintering wasset to be nitrogen atmosphere, and the heat-treatment was carried out inair atmosphere under 800° C. And the evaluation was carried out in thesame way as Example 1. The results of Example 2 according to the presentinvention were shown in table 6.

From table 1, it could be known that there was a relationship betweenthe amount range of Bi (i.e., x) and the Curie temperature. From samplesNO. 1˜10, it could be known that when the amount of Bi was in the rangeof 0.007≦x≦0.125, the Curie temperature shifted to a temperature higherthan 120° C. which is the Curie temperature of BaTiO₃, and the specificresistance at a normal temperature was 10³ Ωcm or less. In addition, itcould be known that the more the amount of x was, the higher the Curietemperature shifted to, and the specific resistance at a normaltemperature tended to increase slightly. In the comparative example 1and example 3 in which the amount range of the Bi element was less than0.007, the specific resistance at a normal temperature was small, butthe Curie temperature did not shift to a temperature higher than 120° C.Moreover, it could be known that in the comparative example 2 andexample 4 in which the amount range of the A element exceeded 0.125, thespecific resistance at a normal temperature was far more than 10³ Ωcm.

TABLE 1 w + z x[mol] y [mol] m Ca[mol] [mol] Si[mol] Mn[mol] Sample NO.0.007~0.125 x~2.0x 0.940~0.999 0.010~0.055 0~0.010 0~0.035 0~0.0015Comparative 0.005 0.01 0.999 0.055 0 0 0 Example 1 1 0.007 0.014 2 0.030.06 3 0.05 0.1 4 0.1 0.2 5 0.125 0.25 Comparative 0.127 0.254 Example 2Comparative 0.005 0.01 0.999 0.055 0 0 0 Example 3 6 0.007 0.014 7 0.030.06 8 0.05 0.1 9 0.1 0.2 10  0.125 0.25 Comparative 0.127 0.254 Example4 specific temperature resistance A coefficient of at 25° C. Tc Na orresistance Sample NO. [Ωcm] [° C.] K α[%/° C.] Note Comparative 450 120Na 27 Curie Example 1 temperature × 1 450 125 27 2 600 135 30 3 700 15532 4 850 195 31 5 850 220 30 Comparative 1.5E+06 — — specific resistanceExample 2 at 25° C.× Comparative 400 120 K 27 Curie Example 3temperature × 6 500 125 28 7 650 150 31 8 700 185 32 9 850 220 32 10 850 245 32 Comparative 1.5E+06 — — specific resistance Example 4 at 25°C. ×

It could be known from table 2 that, the amount range y of A was relatedto the amount range x of Bi element. In addition, A was at least oneelement selected from Na or K. It could be known from Samples No. 1, No.3, No. 5 and No. 12, No. 14, No. 16 that, if the amount y was in therange of x<y≦2.0x, the specific resistance at a normal temperature wouldbe small and the temperature coefficient of resistance α could bemaintained to 20%/° C. or more. In addition, if x was fixed, there was atendency that the specific resistance at a normal temperature decreasedslightly with the increase of y. In the comparative examples 5, 6, 8, 9,11, 12 in which the amount range of y was less than x, the specificresistance at a normal temperature was small, but the temperaturecoefficient of resistance α was less than 20%/° C. Additionally, incomparative example 7, comparative example 10, and comparative example13 in which the amount range of y was larger than 2.0x, the specificresistance at a normal temperature increased and became more than 10³Ωcm. Moreover, it was known that between the case that A was Na and thecase that A was K, there was some difference in the shift amount of theCurie temperature to the higher temperature, but the specific resistanceat a normal temperature and the temperature coefficient of resistance αwere almost the same.

TABLE 2 w + z x[mol] y [mol] m Ca[mol] [mol] Si[mol] Mn[mol] Sample NO.0.007~0.125 x~2.0x 0.940~0.999 0.010~0.055 0~0.010 0~0.035 0~0.0015Comparative 0.007 0.0056 0.999 0.055 0 0 0 Example 5 Comparative 0.007Example 6 12  0.0105 1 0.014 Comparative 0.0154 Example 7 Comparative0.05 0.04 0.999 0.055 0 0 0 Example 8 Comparative 0.05 Example 9 14 0.075 3 0.1 Comparative 0.11 Example 10 Comparative 0.125 0.1 0.9990.055 0 0 0 Example 11 Comparative 0.125 Example 12 16  0.1875 5 0.25Comparative 0.275 Example 13 specific temperature resistance Acoefficient of at 25° C. Tc Na or resistance□ Sample NO. [Ωcm] [° C.] Kα [%/° C.] Note Comparative 1200  125 Na 12 temperature coefficientExample 5 of resistance□ × Comparative 850 14 temperature coefficientExample 6 of resistance□ × 12  500 26 1 450 27 Comparative 1.0E+05 —specific resistance Example 7 at 25° C. × Comparative 1000  155 Na 15temperature coefficient Example 8 of resistance□ × Comparative 900 16temperature coefficient Example 9 of resistance□ × 14  750 28 3 700 32Comparative 1.00E+04  — specific resistance Example 10 at 25° C. ×Comparative 950 220 Na 16 temperature coefficient Example 11 ofresistance□ × Comparative 900 16 temperature coefficient Example 12 ofresistance□ × 16  900 30 5 850 30 Comparative 1.0E+05 — specificresistance Example 13 at 25° C.×

It could be known from table 3 that, the mole ratio m of Ba sites/Tisites was related to the specific resistance at a normal temperature.And it was known that in the samples NO. 5, 17, 18 in which m was in therange of 0.94≦m≦0.999, the specific resistance at a normal temperaturewas small and the temperature coefficient of resistance α shifted to20%/° C. or more. Additionally, the specific resistance at a normaltemperature and the temperature coefficient of resistance α tended toincrease slightly with the increase of m. In the comparative example 14in which m was less than 0.94, the specific resistance at a normaltemperature was as large as 10³ Ωcm and the temperature coefficient ofresistance α was small. Moreover, in the comparative example 15 in whichm exceeded 0.99, the specific resistance at a normal temperature wasmore than 10³ Ωcm and the forming to a semiconductor was insufficient.

TABLE 3 w + z x[mol] y [mol] m Ca[mol] [mol] Si[mol] Mn[mol] Sample NO.0.007~0.125 x~2.0x 0.940~0.999 0.010~0.055 0~0.010 0~0.035 0~0.0015Comparative 0.125 0.25 0.92 0.055 0 0 0 Example 14 17 0.94 18 0.97  50.999 Comparative 1.02 Example 15 specific temperature resistance Acoefficient of at 25° C. Tc Na or resistance Sample NO. [Ωcm] [° C.] K α[%/° C.] Note Comparative 5.E+03 220 Na 2 temperature coefficientExample 14 of resistance × 17 500 35 18 450 35  5 850 30 Comparative1.E+05 — temperature coefficient Example 15 of resistance ×

It could be known from table 4 that, the amount range of the minorcomponent Ca was related to the specific resistance at a normaltemperature. In the samples of No. 5, 19, 20 in which the amount of Cawas in the range of 0.01 mol or more and 0.055 mol or less, the specificresistance at a normal temperature was small and the temperaturecoefficient of resistance α was maintained to 20%/° C. or more.Moreover, the specific resistance at a normal temperature tended toincrease slightly with the increase of the amount of Ca. As for thecomparative example 16 in which the amount range of Ca was less than0.01 mol and the comparative example 17 in which the amount range of Caexceeded 0.055 mol, the specific resistance at a normal temperatureincreased and were more than 10³ Ωcm,

TABLE 4 w + z x[mol] y [mol] m Ca[mol] [mol] Si[mol] Mn[mol] Sample NO.0.007~0.125 x~2.0x 0.940~0.999 0.010~0.055 0~0.010 0~0.035 0~0.0015Comparative 0.125 0.25 0.999 0.008 0 0 0 Example 16 19 0.01 20 0.03  50.055 Comparative 0.058 Example 17 specific temperature resistance Acoefficient of at 25° C.[ Tc Na or resistance Sample NO. Ωcm] [° C.] K α[%/° C.] Note Comparative 5.0E+04 220 Na — temperature coefficientExample 16 of resistance × 19 600 30 20 650 35  5 850 30 Comparative1.0E+04 — temperature coefficient Example 17 of resistance ×

It could be known from the samples of NO. 5, 28˜69 of Table 5 that, if(w+z) which represented the total amount of RE and TM was not largerthan 0.01, there was an effect of decreasing the specific resistance ata normal temperature. Moreover, if balances of the specific resistanceat a normal temperature and the temperature coefficient of resistance αwere considered, (w+z) was more preferred to be 0.001 mol or more and0.005 mol or less. In addition, it was known that in the case that REwas Sm, Gd or Er, and TM was Nb, the specific resistance at a normaltemperature was smaller than that in the cases of other RE and TM.Additionally, as for the comparative examples 18˜30 in which (w+z)exceeded 0.01, the specific resistance at a normal temperature was morethan 10³ Ωcm. Further, from the samples of NO. 64˜69, it could be knownthat even among the cases that the values of (w+z) were the same, thesamples in which RE and TM were added in equal amount had smallerspecific resistances at a normal temperature.

TABLE 5 x[mol] y[mol] m Ca[mol] Si[mol] Mn[mol] Sample NO. 0.007~0.125x~2.0x 0.940~0.999 0.010~0.055 0~0.035 0~0.0015 RE TM  5 0.125 0.250.999 0.055 0 0 Y 28 29 30 Comparative Example 18 31 0.125 0.25 0.9990.055 0 0 La 32 33 Comparative Example 19 34 0.125 0.25 0.999 0.055 0 0Ce 35 36 Comparative Example 20 37 0.125 0.25 0.999 0.055 0 0 Pr 38 39Comparative Example 21 40 0.125 0.25 0.999 0.055 0 0 Nd 41 42Comparative Example 22 43 0.125 0.25 0.999 0.055 0 0 Sm 44 45Comparative Example 23 46 0.125 0.25 0.999 0.055 0 0 Gd 47 48Comparative Example 24 49 0.125 0.25 0.999 0.055 0 0 Dy 50 51Comparative Example 25 52 0.125 0.25 0.999 0.055 0 0 Er 53 54Comparative Example 26 55 0.125 0.25 0.999 0.055 0 0 V 56 57 ComparativeExample 27 58 0.125 0.25 0.999 0.055 0 0 59 60 Nb Comparative Example 2861 0.125 0.25 0.999 0.055 0 0 Ta 62 63 Comparative Example 29 64 0.1250.25 0.999 0.055 0 0 Gd Nb 65 66 67 68 69 Comparative Example 30specific temperature resistance A coefficient w[mol] z[mol] (25° C.) TcNa or of resistance Sample NO. 0~0.01 [Ωcm] [° C.] K α [%/ ° C.] Note  50 0 850 220 Na 30 28 0.001 0 700 31 29 0.005 0 600 31 30 0.01 0 650 31Comparative 0.012 0 4800 11 specific resistance Example 18 at 25° C. ×31 0.001 0 700 220 Na 31 32 0.005 0 600 30 33 0.01 0 650 31 Comparative0.012 0 8000 8 specific resistance Example 19 at 25° C. × 34 0.001 0 700220 Na 30 35 0.005 0 650 29 36 0.01 0 700 30 Comparative 0.012 0 7000 10specific resistance Example 20 at 25 ° C. × 37 0.001 0 750 220 Na 30 380.005 0 650 28 39 0.01 0 700 31 Comparative 0.012 0 4000 12 specificresistance Example 21 at 25° C. × 40 0.001 0 700 220 Na 28 41 0.005 0650 29 42 0.01 0 700 29 Comparative 0.012 0 7000 8 specific resistanceExample 22 at 25° C. × 43 0.001 0 500 220 Na 30 44 0.005 0 550 30 450.01 0 700 30 Comparative 0.012 0 5000 12 specific resistance Example 23at 25° C. × 46 0.001 0 700 220 Na 28 47 0.005 0 600 30 48 0.01 0 650 31Comparative 0.012 0 3000 14 specific resistance Example 24 at 25° C. ×49 0.001 0 700 220 Na 30 50 0.005 0 600 28 51 0.01 0 650 28 Comparative0.012 0 4000 12 specific resistance Example 25 at 25° C. × 52 0.001 0550 220 Na 32 53 0.005 0 550 30 54 0.01 0 600 30 Comparative 0.012 05500 9 specific resistance Example 26 at 25° C. × 55 0 0.001 700 220 Na30 56 0 0.005 700 30 57 0 0.01 700 30 Comparative 0 0.012 12000 8specific resistance Example 27 at 25 ° C. × 58 0 0.001 500 220 Na 28 590 0.005 550 28 60 0 0.01 700 29 Comparative 0 0.012 4000 10 specificresistance Example 28 at 25° C. × 61 0 0.001 700 220 Na 30 62 0 0.005600 30 63 0 0.01 700 28 Comparative 0 0.012 7000 9 specific resistanceExample 29 at 25° C. × 64 0.0025 0.0025 400 220 Na 33 65 0.001 0.004 60030 66 0.004 0.001 600 33 67 0.005 0.005 450 32 68 0.002 0.008 700 30 690.008 0.002 700 30 Comparative 0.006 0.006 11000 8 specific resistanceExample 30 at 25 ° C. ×

It could be known from the samples of NO. 5 and 70 in table 6 that, whenthe atmosphere during sintering was an atmosphere of nitrogen (PO₂=10⁻⁷atm), almost the same performance as that in the case of sintering inair atmosphere could be obtained.

TABLE 6 specific temperature w + z resistance A coefficient x[mol] y[mol] m Ca[mol] [mol] Si[mol] Mn[mol] at 25° C. Tc Na or of resistanceSample NO. 0.007~0.125 x~2.0x 0.940~0.999 0.010~ 0~0.010 0~0.0350~0.0015 [Ωcm] [° C.] K α [%/° C.] Note 5 0.125 0.25 0.999 0.055 0 0 0850 220 Na 30 in air 70 650 30 in N2

DESCRIPTION OF REFERENCE NUMERALS

-   1 PTC thermistor-   2 ceramic body-   3 a, 3 b electrodes

What is claimed is:
 1. A semiconductor ceramic composition comprising asintered body which contains a BaTiO₃ based compound represented by thefollowing formula (1) as a main component,(Ba_(1-x-y-w)Bi_(x)A_(y)RE_(w))_(m)(Ti_(1-z)TM_(z))O₃  (1) wherein, inthe formula (1), A is at least one element selected from Na or K, RE isat least one element selected from the group consisting of Y, La, Ce,Pr, Nd, Sm, Gd, Dy and Er, TM is at least one element selected from thegroup consisting of V, Nb and Ta, w, x, y, z (all the units of which aremol) and m (which is the mole ratio of Ba sites/Ti sites) satisfy thefollowing relationships of (2)˜(5),0.007≦x≦0.125  (2)x<y≦2.0x  (3)0≦(w+z)≦0.01  (4)0.94≦m≦0.999  (5) wherein, said semiconductor ceramic compositionfurther comprises Ca in a proportion of 0.01 mol or more and 0.055 molor less in terms of element relative to 1 mol of Ti sites.
 2. Thesemiconductor ceramic composition of claim 1 further comprising Si in aproportion of 0.035 mol or less in terms of element relative to 1 mol ofTi sites.
 3. The semiconductor ceramic composition of claim 1 furthercomprising Mn in a proportion of 0.0015 mol or less in terms of elementrelative to 1 mol of Ti sites.
 4. A PTC thermistor comprising a ceramicbody which is formed by the semiconductor ceramic composition of claim1, and electrodes which are formed on the surfaces of said ceramic body.5. The semiconductor ceramic composition of claim 2 further comprisingMn in a proportion of 0.0015 mol or less in terms of element relative to1 mol of Ti sites.
 6. A PTC thermistor comprising a ceramic body whichis formed by the semiconductor ceramic composition of claim 2, andelectrodes which are formed on the surfaces of said ceramic body.
 7. APTC thermistor comprising a ceramic body which is formed by thesemiconductor ceramic composition of claim 3, and electrodes which areformed on the surfaces of said ceramic body.
 8. A PTC thermistorcomprising a ceramic body which is formed by the semiconductor ceramiccomposition of claim 5, and electrodes which are formed on the surfacesof said ceramic body.